This invention relates to a mesoporous silica material and to a method of producing same. More specifically, the present invention is directed to a mesoporous silica material (mesoporous silica spheres) having both regularly distributed uniform pores and a regular morphology.
Since 1992 in which MCM-41 was discovered by Mobil Corporation, a great number of studies pertaining to mesoporous materials have been reported. There are recent reports suggesting a possibility of the formation of regularly distributed mesospores and, at the same time, the control of a structure of a micron or millimeter scale on the basis of the above synthesis method. For example, (1) by controlling a mixing ratio of a surfactant to water and a rate of condensation of silica under highly alkaline conditions, a mesoporous silica material which is in a hollow fibrous state having a diameter of 3 .mu.m and a length of 20 .mu.m and which has a shell portion wherein cylindrical mesopores are arranged in a honeycomb-like state is produced. (2) Also produced are sheet-like or hollow spherical porous silica particles having a macro-morphology of a micron order, depending upon a speed of stirring a hydrochloric acid-containing, aqueous CTAB (cetyltrimethylammonium bromide) solution at the time of dropwise addition of mesitylene-containing tetraethyl orthosilicate (TEOS) thereto. (3) Porous silica hard spheres having a particle size ranging from 0.1 to 2 mm are produced by adding tetrabutyl orthosilicate (TBOS) to an aqueous solution containing CTAB and NaOH and by stirring the mixture.
The above mesoporous silica materials have drawbacks with respect to the preparation methods thereof, because the reaction steps are complicated and because a long reaction time is required. Additionally, in (1), there is a defect in the pore structure thereof, because a film-like substance having mesopores changes into a cylindrical form. Moreover, it is not possible to suppress crystallization of fine particles. In (2), it is difficult to efficiently obtain uniform spherical particles, because the macro-morphology of the mesoporous silica materials is sensitive to the stirring speed. Thus, addition of mesitylene is required. In (3), there is a problem that TEOS is not able to be used.